My guess

the red LED marked PWR will light (except for the zero). The green LED marked OK (or ACK in later version) will blink in an irregular pattern to show whenever the Pi reads from the SD card.

Yet this never occured on my Raspberry...

Furthermore, I wonder whether it is because when writing an image (eg using 'DD') I have to ensure that the destination is the entire card and not a partition on it. Indeed the few writing operations on the command line where:

2 Answers
2

so as stated in the comments you mention that after writing all zeros to the sd card using the command

sudo dd if=/dev/zero of=/dev/sdX bs=1k count=2048

You state that when trying to unmount your drive using the command

sudo umount /dev/sda1

that you get an error stating that the device is busy.
With this information I believe that a process is attempting to write to your sd card in the background which is preventing you from unmounting it and is also quite possibly corrupting your sd card write. If you could please now ensure that it is the correct sd card that you are writing to by removing the sd card and using the command

sudo fdisk -l

Then by connecting the sd card and retuning the command listed above that will be the name of your sd card (note the name may change with disconnects). To forcefully unmount the drive you may use the following command listed below:

fuser -km /dev/sda2

k : Kill processes accessing the file.

m : Name specifies a file on a mounted file system or a block device that is mounted. In above example you are using /dev/sda2

Note: The command above may need to be run with sudo
After your SD card has been successfully unmounted, use the command below to write your iso to your sd card.

dd bs=4M if=raspberrypi-img.iso of=/dev/sda2

bs=4M is optional. It stands for Block Size and is used to create larger blocks to write faster, if this does not work for you try bs=1M

Than you for considering my question. I did the command line you gave mequestion to show you them, and edited my , yet I'm nt sure of which sda is the one where the boot is set because of the *
– ThePassengerMay 17 '16 at 12:54

What part are you stuck on, because you do not need the boot column days in any of this sudo fdisk -l to see which dev drive it is. Just run the command, without the Ed card or adapter plugged in.then plug the sd card and and see which new dev drive shows up. If you can't figure it out on your own just share what it says before and after you connect the drive and I'll try and help you figure out which drive it is.OH you many also be looking at the boot * which is the boot hdd and not the sd card
– Mohammad AliMay 17 '16 at 13:04

Please elaborate on which command you get stuck at and why
– Mohammad AliMay 17 '16 at 13:04

I just uploaded what I did with your advises. I think the new dev drive is mmcblk0.
– ThePassengerMay 17 '16 at 13:24

I had this very same problem. I found that it was 3 things. First, try using a different HDMI cable. Then, try following the procedures to re-install the image to your SD card. You can find that on www.raspberrypi.org, and type into the search bar how to install the raspbian image. And if that doesn't work, try changing out the PI unit. I have 3 RPI2B, and I found out that the one I wanted to use was quite abused and contributed to my issues. Trying any one of these combinations will end up with a satisfactory result, it's just time consuming. Your power source COULD be an issue too, but I doubt it. However one whom, is prudent would check on that as well.